Release Reason Mapping; Reason Header - AudioCodes Mediant 2000 User Manual

11.2

Release Reason Mapping

This section describes the available mapping mechanisms of SIP responses to Q.850
Release Causes and vice versa. The existing mapping of ISDN Release Causes to SIP
Responses is described in ''Fixed Mapping of ISDN Release Reason to SIP Response'' on
page 472 and ''Fixed Mapping of SIP Response to ISDN Release Reason'' on page 475. To
override this hard-coded mapping and flexibly map SIP responses to ISDN Release
Causes, use the ini file (CauseMapISDN2SIP and CauseMapSIP2ISDN, as described in
''ISDN and CAS Interworking-Related Parameters'' on page 325) or the Web interface (refer
to ''Configuring Release Cause Mapping'' on page 151).
It is also possible to map the less commonly used SIP responses to a single default ISDN
Release Cause. Use the parameter DefaultCauseMapISDN2IP (described in ''ISDN and
CAS Interworking-Related Parameters'' on page 325) to define a default ISDN Cause that is
always used except when the following Release Causes are received: Normal Call Clearing
(16), User Busy (17), No User Responding (18) or No Answer from User (19). This
mechanism is only available for Tel-to-IP calls.

11.2.1 Reason Header

The device supports the Reason header according to RFC 3326. The Reason header
conveys information describing the disconnection cause of a call:

Sending Reason header:
Reason header is set to the received Q.850 cause in the appropriate message
(BYE/CANCEL/final failure response) and sent to the SIP side. If the call is
disconnected because of a SIP reason, the Reason header is set to the appropriate
SIP response.

Receiving Reason header:
message includes the Reason header, it is sent to the Tel side according to the
following logic:
•
If the Reason header includes a Q.850 cause, it is sent as is.
•
If the Reason header includes a SIP response:
♦
♦
•
When the Reason header is received twice (i.e., SIP Reason and Q.850), the
Q.850 takes precedence over the SIP reason and is sent to the Tel side.
SIP User's Manual
If a call is disconnected from the Tel side (ISDN), the
If a call is disconnected from the IP side and the SIP
If the message is a final response, the response status code is translated to
Q.850 format and passed to ISDN.
If the message isn't a final response, it is translated to a Q.850 cause.
472
Mediant 2000
Document #: LTRT-68809